A typical, high power radio frequency (RF) amplifier device includes a packaged power transistor that is configured to operate at a fundamental operating frequency, f0. For example, FIG. 1 is a simplified conceptual diagram of a typical, high power RF amplifier device 100, and FIG. 2 is a schematic diagram 200 of such an RF amplifier device. As shown, a typical RF amplifier device 100, 200 includes one or more input leads 102, 202, one or more output leads 104, 204, one or more transistors 130, 230, and input-side, fundamental matching circuitry 110, 210. In addition, a device 100, 200 may include bondwire arrays (e.g., in the form of inductances 212, 216) coupling each input lead 102, 202 to the control terminal (e.g., the gate) of each transistor 130, 230, and a bondwire array (e.g., in the form of inductance 240) coupling the output terminal (e.g., the drain) of each transistor 130, 230 to an output lead 104, 204.
The fundamental matching circuitry 110, 210 is configured to provide impedance matching between the input lead 102, 202 and the transistor 130, 230 at the fundamental frequency of operation, f0, of the amplifier device 100, 200. For example, as shown in FIG. 2, the configuration of a typical fundamental matching circuitry 110, 210 may include a T-match circuit that includes two series inductances 212, 216 coupled between the input lead 202 and the control terminal of the transistor 230, and a shunt capacitance 214 between an intermediate node 218 and a ground reference.
For some types of amplifiers, it is desirable to mitigate the impacts of signal energy at harmonic frequencies. Accordingly, some amplifier circuits include harmonic control circuitry, which may reduce or minimize the conduction angle of the output current waveform (i.e., reduce or minimize the overlap between the output current and voltage waveforms). Due to package size limitations and a low gate node impedance at the second harmonic frequency in a high-power device, conventional methods of performing second harmonic frequency control may lead to non-optimal results. Accordingly, circuit and device designers continue to seek different methods and apparatus for providing harmonic frequency control in high-power amplifier circuits and devices.